ELI5: Explain Like I'm 5

Popping

When you move your joints to make a “pop” sound, it’s called popping. It’s like cracking your knuckles or your back. The sound you hear is from gas bubbles in your joint fluid making a little “pop” when they move out of the way. It doesn’t hurt and it can actually feel good to do! Just be careful not to do it too much or too hard because that can make your joints sore.
Related topics others have asked about: